act_anat_prepare_fsl: Fix for FSL4
act_anat_prepare_fsl: Fix for FSL4

It seems the MNI T1 1mm dilated brain mask is not present in FSL4.
Therefore use the 2mm mask if necessary.

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3